1. Field of the Invention.
This invention relates to method and apparatus for injecting samples of material into a high pressure environment. More particularly, the invention pertains to sample injection apparatus for use in liquid chromatography.
2. Description of the Prior Art.
Liquid chromatography pertains to a particular variety of equipment and techniques for analyzing the components of an unknown sample of liquid material, qualitatively and/or quantitatively. According to chromatographic techniques, a column is provided which is packed with a finely divided material. The packing material provided is chosen in accordance with its affinity for attracting certain elements to adsorb, or cling to it. When the sample is forced through the column, each of the components passes through the column in a time pattern which is a function of the degree of tendency of that component to be adsorbed by the packing material. By detecting variations in properties of the substance emerging from the column, and plotting these variations against time, certain information can be derived as to the nature and amount of the components of the unknown sample. For example, the presence of a given component of the sample may be known to effect a change in a particular property of the liquid emerging from the column such that a maximum value of that property will occur at a predetermined time after the sample is introduced into the column. By observing where such peaks occur, the nature of various components of the sample may be determined with a significant degree of certitude and repeatability.
In liquid chromatography, it is customary to introduce the sample into the column immediately previous to the introduction of another liquid, called a carrier, in order to dissolve the sample and drive it through the column. It has been found that if the sample is driven through the column at very high pressure, a consequent reduction in the time for analysis of each sample is observed, due to the more rapid passage of the sample through the column. One of the problems in high pressure chromatography is the need for stopping the flow of the carrier into the column during the introduction of the sample. This need arises because of the inherent difficulties in injecting a second substance into a stream flowing at high pressure. It is difficult to provide high pressure seals which are durable and reliable and which are capable of accomplishing or allowing this function. Also, the necessity for interrupting carrier flow slows down the operation.
In liquid chromatography, it is often very useful to utilize a mechanism containing several cells or separate containers for samples, into which various samples for analysis can be pre-loaded. After preloading, the cells are successively connected to the column and the pressure elevated to inject the sample into the column. This desirability of simultaneously loading multiple samples, and subsequently successively driving them through the column, necessitates the provision of a large number of movable high pressure seals. Such apparatus is inherently quite expensive and difficult to machine, and the seals involved are often of dubious reliability and limited durability.